This invention is directed to low cost, wax-free, hot melt adhesive compositions particularly suitable for such applications as, for example, sealing packaging cartons.
The usual commercial hot melt adhesives are based on a solid, polymeric thermoplastic material, which is compounded with one or more tackifiers and waxes and contains additives such as antioxidants or other stabilizers. The most commonly used tackifiers are hydrocarbon resins, terpenes, terpene/phenolics, coumarone/indene resins, polymerized .alpha.- and .beta.-pinenes, rosin-modified phenolic resins, polymerized rosin, rosin derivatives such as hydrogenated and dimerized rosins, and tall oil rosins. Because of their higher heat sensitivity, tall oil rosins are not normally recommended for use in high quality hot melt adhesive compositions. Wax, which is a low-melting hydrocarbon material, serves as a softening point depressant and the same time as a low cost filler. The usual waxes employed in hot melt adhesive compositions include paraffin waxes, microcrystalline waxes, and synthetic waxes. A hot melt adhesive composition naturally must be heat stable. Decomposition of any component on heating or exudation at any temperature would make such a composition useless. Similarly, crystallization of the adhesive on cooling would be very undesirable. While many high performance, high cost hot melt adhesives are commercially available, it has been difficult to formulate a low cost hot melt adhesive composition capable of providing high strength bonds. For example, a low cost adhesive might use cheap processing oils instead of expensive waxes, but oils have not met with good acceptance because of their tendency to exude.